The manufacture of petroleum coke for anode production, particularly for the manufacture of aluminum, is well known. U.S. Pat. No. 4,718,984 to McConaghy, Jr. et al. describes the prior art process of calcining petroleum coke at high temperatures to drive off volatile hydrocarbons and moisture. The calcined product may then be used to produce anodes for aluminum manufacture and, in cases where the coke is of a premium quality, it can be used for manufacture of graphite electrodes useful in electric arc steelmaking processes.
The petroleum coke is generally calcined at temperatures between 1250.degree. and 1400.degree. C. to reduce its volatile content and establish electrical conductivity. Calcination generally takes place in a rotary kiln. Upon exiting the kiln, the hot coke is usually cooled with a water spray to avoid unnecessary reaction of the carbon with oxygen in the air as shown in the following reaction: EQU C+O.sub.2 .fwdarw.CO.sub.2.
Alternatively, coke quenching can be performed using other quenching media such as water baths, steam, inert gases or a combination thereof.
The quenched coke is then manufactured into anodes as is well known in the prior art.
One of the problems inherent in the manufacture of coke product is burning or combustion thereof when the coke is exposed to air after being subjected to high temperatures. Because of this airburning tendency, the coke product is quenched or cooled to below its ignition temperature.
U.S. Pat. No. 3,959,084 to Price recognizes this problem and proposes a two step cooling process using both inert gases and water quenching.
A similar airburning problem exists when the coke is formed into anodes, especially for aluminum production. Since these anodes operate in aluminum reduction cells at temperatures approximating 950.degree. C., the anodes can be consumed by oxygen in the air if not properly covered.
In aluminum reduction cells, the anode is covered by an electrolytic bath typically including alumina and cryolite. This covering material not only provides a source of aluminum for the reduction cell but also protects the anode against premature oxidation or airburning. However, the electrolytic bath may not always cover the anode and protect it from airburning. Exposure of the anode to air in the high temperature environment of the aluminum reduction cell can adversely affect the production of aluminum as well as anode life.
In view of the problems associated with maintaining a cover on the anode of an aluminum reduction cell, a need has developed to find alternative ways to reduce or prevent the airburning of anodes in these types of high temperature manufacturing processes.
In response to this need, the present invention provides a method of treating the petroleum coke used in making these types of anodes which minimizes the exposure of the anode to air regardless of the presence of a protective covering.